| 초록 |
Carbon nanotubes have drawn attention as one of the most promising emitter materials ever known not only due to their nanometer-scale radius of curvature at tip and extremely high aspect ratios but also due to their strong mechanical strength, excellent thermal conductivity, good chemical stability, etc. Some applications of CNTs as emitters, such as X-ray tubes and microwave amplifiers, require high current emission over a small emitter area. To operate the high current density, CNT emitter should be optimally fabricated in terms of material properties and morphological aspects: highly crystalline CNT materials, low gas emission during electron emission in vacuum, optimal emitter distribution density, optimal aspect ratio of emitters, uniform emitter height, strong emitter adhesion onto a substrate, etc. Adhesion of emitters is one of the most important parameters to be secured for high current field emission. So, we attempted a novel approach to fabricate CNT emitters to meet some of requirements described above, including strong emitter adhesion. In this study, CNT emitters were fabricated on a metal mesh by filtrating an aqueous suspension containing both highly crystalline thin multiwalled CNTs and thick, entangled multiwalled CNTs. Additionally, we filtrated cobalt-nickel metal-organic solution to form oxide-nickel oxide layers between CNT networks to improve an adhesion of CNTs with different diameters and metal mesh. The CNT emitters without and with the oxide additives were characteristic of the turn-on electrical fields of 0.59, 1.29 V/μm and the current density of 188, 288 mA/cm2 at 4 V/μm, respectively, over a sample size 0.5 x 0.5 cm2. The CNT emitters with oxide additives were more stable in the high current operation. We expected the CNT emitters with oxide additives to be the promising electron sources of high current emission capability, for example, for x-ray generators and microwave amplifiers. |
